1. Field of the Invention
The present invention relates to a color image reading device for use in a color facsimile machine, color scanner, or the like, wherein an original color image is separated into different color data which are detected using a CCD sensor.
2. Description of the Prior Art
The prior art color image reading devices can be divided typically into two types, which are:
(1) a type using a white lamp as a light source, in which three different filters red, green and blue, (R, G, B) mechanically replace one after the other sequentially in front of a CCD array to separate the color image into different colors; and
(2) a type using a white lamp as a light source, in which three CCD arrays provided with filters R, G, B, respectively, are provided to separate the color image into different colors.
According to the first type, it is very difficult to change the filters rapidly. According to the second type, three different colors are detected at different places where the three CCD arrays are positioned. Therefore, the exact matching of the three color images is very difficult.
To solve the above problem, another type of color image reading device has been proposed which employs three fluorescent lamps for emitting three color lights, red light, green light and blue light, which are turned on sequentially one at a time, and one CCD array for receiving red light image, green light image and blue light image at different times.
However, a fluorescent lamp generally has four strong line spectrums at about 405 nm, 436 nm, 546 nm, and 587 nm, due to mercury contained therein. These line spectrums must be deleted, or otherwise the color separation can not be done properly with a desired result. Of the four line spectrums, the 405 nm and 436 nm line spectrums can be deleted easily using a suitable filter. However, the 546 nm and 587 nm line spectrums are located in a spectrum region of the green fluorescent lamp and, therefore, these line spectrums can not be deleted by the use of filters. Moreover, the presence of 546 nm and 587 nm line spectrums at places within the spectrum region of the green fluorescent lamp, but off from the peak point thereof will adversely affect the separation of green data from CCD output.